gles: Abort event loop on key press

If a keypress event has been detected, return false, signalling to the
caller to quit the main loop.

Signed-off-by: Thierry Reding <thierry@gilfi.de>
gles: Add gles-cube test program

This test program is an implementation of the classic rotating cube
example.

Signed-off-by: Thierry Reding <thierry@gilfi.de>